Rows of huge tanks full of chemical solutions storing energy generated from massive solar and wind farms and powering whole cities: It’s a landscape that millennials might very well equate with the new normal.
Batteries will power this new paradigm, and they won’t necessarily all be lithium-ion batteries. The flow battery is staking a claim in the renewable energy world of the future.
What are flow batteries? They are systems of two connected tanks, both containing electrolyte liquids: one with a positively charged cathode and the other with the negatively charged anode, just like a lithium-ion battery. Electricity passes from one electrolyte liquid to the other via a membrane between the tanks.
Rechargeable like lithium-ion batteries, flow batteries have longer lives because the electric current flowing from tank to tank does not degrade the membrane. True flow batteries are also called redox flow batteries, after the two reactions they utilize: reduction, or a gain of electrons, and oxidation, or loss of electrons from electrolyte liquid to electrolyte liquid.
The main problem with redox flow batteries is that the most popular types among them rely on vanadium, which is a costly material. But with all the innovation going on in the battery space, it was only a matter of time before someone announced a breakthrough. Scientists from the University of Southern California have developed a redox flow battery that uses cheap, sustainable materials.
What the USC team used was a solution of iron sulfate for one electrolyte and a solution of a compound called anthraquinone disulfonic acid, or AQDS for short. Iron sulfate is cheap and widely available: a waste product from mining. AQDS, for its part, “can be manufactured from any carbon-based feedstocks, including carbon dioxide,” according to study co-author Surya Prakash.
Few things can be better than a battery that uses an electrolyte made from carbon dioxide, especially if that battery is cheap to make and has a longer life than a lithium-ion competitor. This longer life is important. If the world is serious about going renewable, we would need long-lasting energy storage systems to supply reliable electricity. Lithium-ion batteries are not particularly long-lasting. The new redox flow battery, according to its authors, can deliver on durability, too.
“To date, there has been no economically viable, eco-friendly solution to energy storage that can last for 25 years,” says the lead author of the study, chemistry professor Sri Narayan. “Lithium-ion batteries do not have the long-life and vanadium-based batteries use expensive, relatively toxic materials limiting large-scale use. Our system is the answer to this challenge. We foresee these batteries used in residential, commercial and industrial buildings to capture renewable energy.”
There seems to be a push to develop what some have called the second generation of flow batteries in response to the increase in renewable power generation capacity and plans for a complete renewable shift in some economies.
Flow batteries appear to be much easier to scale for utility-grade energy storage and their developers are now focusing on cheap and abundant materials such as iron-containing compounds as well as eco-friendly, non-corrosive solutions. It sounds like flow batteries could give us the Holy Grail of renewable energy: reliable, long-life storage.
There are already forecasts that flow batteries could overtake lithium-ion tech in the future. One recent report from business intelligence firm IDTechEx, cited by Energy Storage News, noted there was about 70 MW/250 MWh in redox flow battery storage capacity deployed to date, all in medium to large-scale projects. Deployments, however, are set to increase thanks to the batteries’ fast response time, scalability, and not least, their much easier recyclability than lithium-ion batteries.
The report confirms an earlier forecast, also reported by Energy Storage News, this time from Navigant. The research company noted that despite a slow start, redox flow batteries were now gaining on lithium-ion as the technology advances. It was about time, too. Redox flow battery technology has been live for decades, but its reliance on expensive vanadium was pulling it back from mass adoption.
This is good news because the world will be needing a lot of energy storage once this pandemic is over, and things begin to return to normal, and once we start talking about our carbon footprint again. California alone will need energy storage capacity of as much as 1 GW by 2026 if it is to hit its renewable power targets. The combination of low cost, reliability, durability, and, very importantly, recyclability of all components, will not go unnoticed.
IDTEchEx expects the redox flow battery market, including the costly vanadium-suing batteries, to grow at an impressive annual rate of 30 percent over the next few years. This should sound an alarm with lithium-ion battery developers. Times may well be a-changin’ for the dominant battery technology.